1. Field of the Invention
This invention relates to a semiconductive laser device for optical information processing and optical communication.
2. Description of The Related Art
Semiconductive devices used in optical information processing and optical communication should have a stable oscillation frequency relative to the variation in temperature and/or optical output. In ordinary Fabry-Perot type semiconductive devices, there is no difference between the threshold gains in the oscillatory longitudinal modes or there is no selectivity in wavelength, so that the oscillation wavelength is substantially determined by a gain peak wavelength of an active layer. The gain peak wavelength of the active layer depends greatly on the temperature, resulting in a great variation of the oscillation wavelength depending on the temperature. In order to solve this problem, it is necessary to add a difference in the threshold gain between the respective longitudinal modes. To this end, there has been conventionally used a distributed feedback structure as shown in FIG. 1. In the figure, there is shown a double-hetero structure comprised of an active layer 3 and clad layers 2, 5 wherein a guide layer 4 is provided between the active layer 3 and the clad layer 5. A diffraction grating 16 is also provided between the guide layer 4 and the clad layer 5. The longitudinal modes in the vicinity of the Bragg wavelength which is determined from a diffraction grating cycle and a refractive index are such that the reflection with the diffraction grating is increased with a lowering of the threshold gain of the laser oscillation. Accordingly, a difference in the threshold gain is added to the respective longitudinal modes, ensuring a stable oscillation wavelength relative to the variation in temperature and/or optical output.
However, the distributed feedback structure is very difficult to fabricate and is not advantageous from the industrial viewpoint.